The ubiquity of high-performance mobile devices, such as smartphones and tablets, has the potential to significantly broaden and improve the methods of data collection used in the biobehavioral sciences. Contemporary mobile devices are capable of highly engaging and millisecond accurate stimulus presentation, reaction time measurements, and remote data retrieval. Yet despite these capabilities, their potential as a research tool remains largely unrealized because there is no existing end-to-end solution for conducting behavioral research. The proposed Paradigm for Mobile platform will be the first complete stimulus presentation system for mobile devices suitable for millisecond accurate biobehavioral research. Our platform will enable scientists to create engaging, portable, and millisecond accurate experiments and assessments for a wide range of basic and clinical research. For example, in developmental research, the platform's ability to use the more naturalistic responses available on these devices (e.g. shake, spin, and swipe) will help address issues of task completion in age groups such as toddlers whose limited motor coordination and attention span prohibit the use of traditional desktop computer-based experiments. The platform's flexibility, accuracy and low cost will also allow it to serve as a replacement for expensive and inflexible neurocognitive assessment tools often used in clinical research. Further, it will offer the ability to securely upload experiment results to a cloud based storage system and issue repeated reminders to participants making it well-suited for remote data collection. For example, in large-scale longitudinal studies, which are often conducted over wide geographical areas, the platform will be able to facilitate self-administered assessments. In Phase I we will develop a prototype of the platform (Aim 1) that is able to run experiments in Apple's iOS environment (for iPhone, iPod and iPad). We will demonstrate the platform's timing accuracy using a comprehensive suite of benchmarks which, when published, will be the first study to measure the timing capabilities and suitability of mobile devices for use in the biobehavioral sciences (Aim 2). Finally, we will conduct real world tests of our prototype by running small-scale studies with preschoolers and adults in two different NIH funded laboratories (Aim 3). These studies will allow us to characterize the overall suitability and performance of our prototype, establishing a foundation for further development and broader device support in Phase II. The commercialization of this system would have a broad impact on biobehavioral research by improving the quality and quantity of data collected from key populations, and enabling new modes of continuous, longitudinal data collection.